The ultimate goals of this project are to 1) identify and characterize ion transport pathways in the ileum; 2) to determine how these transporters are regulated, and altered in diarrheal diseases; and 3) to determine the role of anion exchange in organic acid transport by the colon. We will separate villus cells from crypt cells in the ileum using intra-arterial and intraluminal perfusion of calcium chelators. We will prepare brush border and basolateral membranes from these two cell populations using cation precipitation and sucrose density gradient centrifugation techniques. We will then identify and characterize ion transport pathways on each membrane from both crypt and villus cells using the rapid filtration technique and fluorescent probes. Studies to determine if modifier sites are present on a given transporter, that can allosterically activate the transporter, will be performed. After having identified normal transport pathways, we will determine how they are regulated and altered in pathological states. Animal models of diarrhea will include coccidia-infected animals, diabetic animals, glucocorticoid-depleted animals, and 6-OH-dopamine treated animals. The effect of enterotoxins and neurohumoral agents known to affect ion transport will be determined. The effect of protein kinases will be determined. Finally, the role of anion exchange in organic acid transport by the colon will be determined.